Reduction gear of electronic wristwatch with stepping motor and sweep second hand

ABSTRACT

The reduction gear of an electronic wristwatch comprises three concentric output shafts adapted to be rotated at different speeds and operatively connected with each other and with the shaft of a stepping motor through gear wheels. A shaft making one revolution per hour has mounted thereon a friction wheel and a bearing means made in the form of a supporting bush press fitted in a bore of the plate of the wristwatch. The bush is mounted so that a portion thereof projects from the plate toward the bridge of the wristwatch, coordinated with respect to the plate and attached thereto by threaded means. The shaft passes freely through a bore in the supporting bush and is restricted from an unlimited axial displacement in one direction by an end face of the supporting bush, and in the other direction by the end face of that pinion which is mounted on the shaft with interference fit. The reduction gear of an electronic wristwatch can be used by the watch-making industry in the production of quartz wristwatches having a stepping motor, and of like timepieces.

FIELD OF INVENTION

The present invention relates to electronic wristwatches having astepping motor and an analog type of indication, and more particularlyit relates to the reduction gear of an electronic wristwatch having astepping motor and a sweep second.

DESCRIPTION OF THE PRIOR ART

There is known a reduction gear of an electronic wristwatch, /cf. aprospectus No. 850 avialable from Citizen Watch Co Ltd for wristwatchmodel 85XX/, comprising three concentric output shafts adapted to rotateat different speeds, one of these shafts being adapted to make one fullrevolution per hour and having mounted threron a friction wheel, theshafts being drivingly connected through gear wheels with one anotherand with a stepping motor, and a bridge coordinated relative to a plateand secured thereon by threaded means. One of the three concentricshafts carries the second hand, another shaft carries the minute hand,and the third shaft carries the hour hand.

The shaft adapted to make one revolution per hour has one of itsbearings arranged in the frame plate while its other bearing is mountedin an auxiliary bridge accommodated in a counterbore provided in theplate on that side thereof which faces the main bridge of the reductiongear. The incorporation of the auxiliary bridge inadvertently results inan increased height of the reduction gear, and, hence, of the entiremovement of the timepiece, which is contrary to the present-day trend inmaking watches of the type being described. The additional counterborein the plate complicates the manufacture of the plate, and the use ofthe auxiliary bridge further complicates the assembling of the reductiongear, on account of the necessity of positioning and securing an extrapart. Furthermore, the friction torque is produced by two pairs ofperpendicular surfaces which are not relatively adjustable, which alsosubstantially complicates the assembling and adjustment of the reductiongear.

There is further known a reduction gear of an electronic wristwatch withanalog type of indication, (cf. FRG application No. p 2003045 9-31published on Jan. 23, 1970, Int. Class G04 C 3/00) comprising threeconcentric output shafts adapted to rotate at different speeds, of whichone shaft is provided with a bearing press-fitted in a bore in the plateand adapted to make one revolution per hour, this shaft carrying afriction wheel; the three shafts being drivingly connected with oneanother and with the shaft of a stepping motor through gear wheels. Theframework of the reduction gear includes a bridge coordindated withrespect to the plate and secured thereon by threaded means.

In this known reduction gear the shaft adapted to make one revolutionper minute is the last one in the drive chain, which necessitates anadditional friction member without which normal operation of thereduction gear is practically impossible. The incorporation of thisfriction member which is permanently under load adversely affects theefficiency of the reduction gear. Another important feature of thisreduction gear is that its gear wheels between the shafts making,respectively, one revolution per hour and one revolution per minute areaccommodated in counterbores on both sides of the plate. Consequently,the plate is of a complex configuration, which means that it islabour-consuming to manufacture, and also that it complicates theautomation of the process of assembling the reduction gear. Moreover, asthe shaft making one revolution per minute has only one bearing, theoperation of setting thereon the second hand also becomes complicated.

The closest one to the reduction gear of the present invention is areduction gear of electronic wristwatch having a stepping motor and asweep second, disclosed in French application No. 2108200 Cl 04C 3/00.This reduction gear comprises three concentric output shafts adapted torotate at different speeds, one of the shafts being provided with abearing in the form of a supporting bush press-fitted in a bore in theplate, this shaft making one revolution per hour and having mountedthereon a friction wheel; the three shafts being drivingly connected toone another and to the shaft of a motor through gear wheels; thereduction gear further including a bridge coordinated with respect tothe plate and secured thereon by threaded means.

Same as in the two abovedescribed types of the reduction gear, in thelast-mentioned reduction gear the plate has complex counterbores andmilled areas on both sides, which makes its manufacturelabour-consuming; besides, the unadjustable friction member complicatesthe assembling of the reduction gear its adjustment and repair.Moreover, the reduction gear comprises an auxiliary bridge for one ofthe bearings of an intermediate shaft, accommodated in a counterbore ofthe plate on its dial-facing side, which complicates the assembling andadjustments of the reduction gear still further.

Thus, among the common features of the above three types of thereduction gear is the structural intricacy of the plate which accountsfor up to 50 percent of the total labour consumed in the manufacture andassembling of the reduction gear, and this affects the effectiveness ofthe production technology; in addition with the friction coupling beingunadjustable, the manufacture and assembling of the reduction gearbecomes complicated, particularly, when thin wristwatches aremanufactured.

SUMMARY OF THE INVENTION

It is an object of the present invention to create a reduction gear ofan electronic wristwatch having a stepping motor and a sweep secondwherein the structure of the shaft support, accommodated in thewristwatch plate, with the shaft making one revolution per hour,provides higher production technology and simplicity in assembling, aswell as reduction of its overall height.

This object is attained by a reduction gear of an electronic wristwatchhaving a stepping motor and a sweep second, comprising three concentricoutput shafts adapted to rotate at different speeds. One of the shaftsis provided with a bearing in the form of a supporting bush press-fittedin a bore in a plate, this shaft being adapted to make one revolutionper hour and to carry a friction wheel. The shafts are drivinglyconnected to one another and to the shaft of the motor through gearwheels and a bridge coordinated with respect to the plate and securedthereon by threaded means. This reduction gear, in accordance with thepresent invention, has the shaft adapted to make one revolution per hourfreely passing through a bore in the supporting bush, the supportingbush being press-fitted in the bore of the plate so that a portionthereof projects from the plate toward the bridge, said shaft beingprevented from unlimited axial displacement in one direction by an endface of the supporting bush and in the other direction by an end face ofthat gear wheel which is mounted on this shaft with an interference fit.

It is expedient that the portion of the supporting bush, projecting fromthe plate, should be accommodated in a counterbore provided in a flangeof the shaft freely passing through the bore of the supporting bush.

It is further expedient that the friction wheel should be located in aplane extending intermediate that end face of the supporting bush, whichprojects from the plate, and the other end face thereof.

It is further expedient that the friction wheel should be mounted forfree rotation on the flange of the shaft freely passing through the borein the supporting bush, and should be adapted for friction engagementwith respective parallel end faces of two elements coaxial with theshaft, these faces facing each other.

It is still further expedient that one of said two elements should be asplit bush mounted with an interference fit on the flange on the shaft,and that the other element should be an annular shoulder provided on theflange of the shaft.

It is still further expedient that the gear wheels through which theshaft of the stepping motor is operatively connected with the shaftfreely passing through the bore of the supporting bush should bearranged that side of the plate, which faces the bridge.

It is also expedient that in a reduction gear wherein the shaft adaptedto make one revolution per minute is mounted in bearings, in accordancewith a preferred embodiment of the invention, this shaft should passthrough a bore in the shaft freely passing through the bore in thesupporting bush.

It is preferable that the supporting bush press-fitted in the bore ofthe plate be coordinated with respect to the bridge by at least twothreaded studs attaching the bridge to the plate.

It is also expedient that each of the studs should have a distancebetween two most remote points on its end face surface, coordinating theplate, at least equal to the spacing of the geometric axes of any twoadjacent shafts.

If the shaft adapted to make one revolution per hour freely passesthrough the bore in the bush press-fitted in the plate on itsbridge-facing side, this shaft can be put in place while assembling thereduction gear, likewise from the side of the bridge, whereby the entiregearing between this shaft and the shaft adapted to make one revolutionper minute may be arranged on one side of the plate, facing the bridge.This enables to do without several complex counterbores and milled areasin the plate, i.e. to simplify both the structure of the plate and itsmanufacture. The coordination and securing of the bridge on the plate bytwo or more threaded studs makes the above advantageous feature evenmore obvious.

The restriction of axial play of the shaft adapted to make onerevolution per hour is effected in the herein disclosed reduction gearin the simplest way possible, with only two dimensions defining thedegree of its play, which yields substantial labour saving in theassembling of the reduction gear. The adjustability of the frictionmember makes this advantageous feature more pronounced. At the sametime, the structure of the entire assembly of output shafts enablessignificantly reduction of the overall height of the reduction gear.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be further described in connection with its preferredembodiments, reference being made to the accompanying drawings, wherein:

FIG. 1 is a longitudinal section of a reduction gear of an electronicwristwatch having a stepping motor and a sweep second embodying theinvention,

FIG. 2 is an enlarged longitudinal section of a reduction gear shaftassembly, with the shaft adapted to make one revolution per hour havingan integral flange; and

FIG. 3 is a view similar to FIG. 2, but with a composite flange of theshaft adapted to make one revolution per hour.

PREFERRED EMBODIMENTS OF THE INVENTION

In the drawings, the reduction gear of an electronic wristwatch having astepping motor and a sweep second includes a pinion 1 (FIG. 1) mountedon a shaft 2 of a stepping motor 3, this shaft 2 being the input shaftof the reduction gear. The pinion 1 meshes with an idler 4 fitted on ashaft with a pinion 5 which, in turn, meshes with a second gear 6. Thegear 6 is fitted on a shaft of the central or sweep second pinion 7adapted to make one revolution per minute and meshing with an idler 8.The idler 8 is fitted on the shaft of a pinion 9 which meshes with acentral friction wheel 10, the friction wheel 10 being received for freerotation on a flange 11.

The flange 11 is mounted with interference fit on a hollow shaft 12adapted to make one revolution per hour. In the embodiment illustratedin FIG. 2 the flange 11 is an integral part mounted on areduced-diameter portion of the shaft 12. In the embodiment illustratedin FIG. 3 the flange 11 is of a composite structure. In this embodimentthe flange 11 is defined by a cylindrical shoulder 12a of the shaft 12and an L-shaped part, press-fitted on this shoulder 12a. Alternatively,the flange 11 can be fully integral with the shaft 12, as it is shown inFIG. 1. In any case, the flange 11 has an inner end face 11a adapted torestrict the axial play of the shaft 12.

Made in the outer or external surface of the flange 11 is an L-shapedgroove defining two perpendicular surfaces, i.e. a cylindrical surface11b and the face surface of an annular abutment 11c of the flange 11.The former of the two surfaces supports the wheel 10 radially, and thelatter supports it axially. The end of the hollow shaft 12, projectingtowards the dial (not shown), has mounted thereon a driver cannon pinion13 abutting against a shoulder 12b and meshing with a minute wheel 14.The minute wheel is fitted on a pinion 15 meshing with an hour wheel 16.The hour wheel is integral with a hollow shaft 16a adapted to make onerevolution in twelve hours and carrying an hour hand 17. The bush 13a ofthe driver cannon pinion 13 carries a minute hand 18; and the end of theelongated lower journal of the shaft of the central second pinion 7passing through the hollow shaft 12 carries a second hand 19. Thus, theshaft of the central second pinion 7 and the hollow shafts 12 and 16a,concentric therewith, are the three output shafts of the reduction gear,adapted to rotate at different speeds and connected operatively with oneanother and with the shaft 2 of the stepping motor 3 through gearwheels. The upper journal 5a of the pinion 5, the upper journal 7a ofthe pinion 7 and the upper journal 9a of the pinion 9 are supported,respectively, in jewel bearings 20, 21 and 22 press-fitted in therespective bores of a bridge 23 of the reduction gear. The lower journal5b of the pinion 5 and the lower journal 9b of the pinion 9 arerespectively supported in jewel bearings 24 and 25 press-fitted in therespective bores in a plate 26; and the lower journal 7b of the pinion 7is supported in a jewel bearing 27 press-fitted in the bore of the shaft12.

Press-fitted in the central bore 26a of the plate 26 (FIG. 3) is a bush28 acting as a bearing for the shaft 12 which freely passes through thebore of the bush 28. The elongated portion 28a of the bush 28 projectsfrom the plate 26 toward the bridge 23 so that the inner cylindricalsurface 28b of the bush 28, acting as a radial bearing for the shaft 12,is sufficiently developed in the axial direction. It is preferable thatthe height "h" of the bush 28 should be at least equal to the externaldiameter "D" of the shaft 12.

The bush 28 has a radial shoulder 28c engaging the plate 26, whichprevents incidental withdrawal of the bush 28 when the minute pinion 13is removed in the course of disassembling the reduction gear, e.g.during repairs of the watch. The elongated cylindrical portion 28a ofthe bush 28 is accommodated in an internal counterbore 11d of the flange11, the upper end face 28d of the bush 28 serving as the axial bearingof the hollow shaft 12, and the lower end face 28e thereof acting as theaxial bearing of the pinion 13; and, with the pinion 13 being mounted onthe shaft 12 with interference fit, the end face 28e of the bush 28 is,in fact, an axial bearing of the shaft 12. Therefore, the value Δ of theaxial play of the shaft 12 and, hence of the central wheel 10 and of thedriver cannon pinion 13 is defined by manufacturing tolerances of buttwo dimensions, viz. the height "h" of the bush 28 and the spacing Hbetween the end face 11a of the flange 11 and the shoulder 12b of theshaft 12.

Mounted with interference fit onto the cylindrical surface 11b of theflange 11 is a split bush 29 adapted for friction engagement with theupper face 10a of the central friction wheel 10 of which the lower face10b is adapted for friction engagement with the end face of the angularabutment 11c of the flange 11, which is parallel with the end face ofthe bush 29. By an axial adjustment of the split bush 29, it is possibleto vary the deflection of the central friction wheel 10, and thus toadjust the value of the friction torque.

The wheel 10 has its upper face 10a spaced from the plate 26 by adistance B which is equal to or less than the spacing B' of the plate 26from the upper face 28d of the bush 28. Preferably, B<B' (see FIG. 3)which is attained by the upper portion 28a of the bush 28 being receivedin the inner counterbore 11d of the flange 11, and the wheel 10 beingpositioned on the external L-shaped groove of the flange 11. Thus, thewheel 10 is in a plane extending intermediate the end faces of the bush28, i.e. within the bearing, and the radial force between idler pinion 9and central friction wheel 10 is applied intermediate the bearing orsupport surfaces of the shaft 12. The bearing surfaces of the shaft 16aof the hour wheel 16 are the outer cylindrical surface of the bush 13aof the driver cannon pinion 13 and its face 13b, and also the side of adial (not shown), facing the plate 26. The radial bearing of the shaftof the minute pinion 15 is a pin 30 tightly fitted in a bore in theplate 26; the upper axial bearing of this pinion 15 is the plate 26proper, while its lower axial bearing is either a cock (not shown), orthe plate of the calendar (not shown).

As it can be seen in FIG. 1, the plate 26 has neither counterbores normilled areas on its side facing the bridge 23. Made in the plate 26 onthis side are only bores 26c each having fitted therein a cylindricalprojection 31a of a threaded stud 31, i.e. a stud having a threadedbore, the other cylindrical projection 31b of this stud 31 serving forcoordinating or positioning the bridge 23 on the end face of thisprojection. The spacing "d" between any two most remote points of thebridge positioning end face 31c of the stud 31 is substantially equal tothe spacing A between the geometric axes of any two adjacent shafts ofthe reduction gear, as it is shown in FIG. 1, e.g. the shafts of thepinion 9 and pinion 7. Preferably, α<A.

The stud 31, preferably, is circular in plan view. However, in practicalembodiments of the invention, this shape may be different, e.g. oval,square, triangual, etc.

There may be any number of threaded studs 31, but not less than two. Itis preferable that two studs should be incorporated, because in thiscase the required accuracy of coordinating the bridge 23 with respect tothe plate 26 is attained in the simplest way.

The bridge 23 rests on the upper end faces 31c of the studs 31 and hasits bores received on the respective projections 31b of studs 31, thebridge 23 being fastened to these studs 31 by screws 32, in which mannerthe bridge 23 is coordinated or positioned with respect to the plate 26.

The jewel bearings 20, 21 and 22 in the bridge 23 and the jewel bearings24 and 25 in the plate 26 are preferably press fitted, flush with therespective surfaces of the bridge 23 and plate 26, facing each other.

The bearings 20, 21, 22, 24 and 25 of the embodiment, illustrated inFIG. 1, are of jewel bearing type; however, they may be of differenttype and materials, e.g. of the self-lubricating type; it is alsopossible that gauged bores proper in the plate 26 and in the bridge 23may serve as bearings.

The operation of the reduction gear of an electronic-watch having astepping motor and sweep second, embodying the invention, is obvious tothose skilled in the art.

Industrial Applicability

The reduction gear of an electronic wristwatch having a stepping motorand a sweep second can be most effectively used by the watch-makingindustry in the production of guartz wristwatches with a stepping motor,and of like timepieces.

What we claim is:
 1. A reduction gear of an electronic wristwatch havinga stepping motor and a sweep second, comprising three concentric outputshafts rotating at different speeds, a first one of the shafts beingprovided with a bearing in the form of a supporting bush press-fitted ina bore in a wristwatch plate, said first shaft making one revolution perhour and supporting a friction wheel, the shafts being drivinglyconnected to one another and to a shaft of the stepping motor throughgear wheels and a bridge coordinated with respect to the plate andsecured thereon by threaded means, wherein the improvement comprises thefirst shaft freely passing through a bore provided in the supportingbush, the supporting bush being press-fitted in the bore of the plate sothat a portion of said supporting bush projects from the plate towardsthe bridge, said shaft being prevented from unlimited axial displacementin one direction by the end face of the supporting bush and in the otherdirection by the end face of a gear wheel which is mounted on said firstshaft with an interference fit.
 2. A reduction gear according to claim1, wherein the portion of the supporting bush projecting from the plateis accommodated in a counterbore provided in a flange of the shaftfreely passing through the bore of the supporting bush.
 3. A reductiongear according to claim 1, wherein the friction wheel is located in aplate extending intermediate an end face of the supporting bush whichprojects from the plate and the other end face.
 4. A reduction gearaccording to claim 1 wherein the friction wheel is mounted for freerotation on the flange of the shaft freely passing through the bore inthe supporting bush and is in friction engagement with respectiveparallel end faces of two elements coaxial with the shaft, these facesfacing each other.
 5. A reduction gear according to claim 4, wherein oneof said elements is a split bush mounted with an interference fit on theflange of the shaft, the other element is an annular shoulder providedon the flange of the shaft.
 6. A reduction gear according to claim 1wherein the gear wheels, through which the shaft of the stepping motoris operatively connected with the shaft freely passing through the boreof the supporting bush, are arranged on that side of the plate facingthe bridge.
 7. A reduction gear according to claim 1 wherein the firstshaft is mounted in bearings, one of the bearings of the first shaftbeing located in the bore of the shaft freely passing through the borein the supporting bush.
 8. A reduction gear according to claim 1 whereinthe supporting bush press-fitted in the bore of the plate is coordinatedwith respect to the bridge by at least two threaded studs attaching thebridge to the plate.
 9. A reduction gear according to claim 8, whereineach of the studs has a distance between the two most remote points onits end face surface coordinating the plate at least equal to thespacing of the geometric axes of any two adjacent shafts of the gears.